Various circuit arrangements have been proposed to operate 6, 12 or 24 V halogen incandescent lamps from power networks, supplying, for example, alternating power at 220 V, 50 Hz, or 110 V, 60 Hz. The cited literature reference describes various circuits of this type. Such electronic circuits, which frequently are referred to as "electronic transformers", permit the operation of low-voltage lamps, for example halogen incandescent lamps, by a brightness control element, which is customarily referred to as a dimmer. Dimmers, as usually used, operate by phase controlling the supply power. Use of conventional, commercial dimmers, with phase control, leads in many circuits to abrupt hard switching from OFF to ON condition, which places great stresses on the electronic lamp circuit and, under some conditions, leads to an intermittent or flickering lamp operation.
Typical electronic transformer circuits utilize a transistor switching arrangement, providing high-frequency output by alternately switching two transistors, connected in a self-starting half-bridge oscillator circuit. The transistors are connected to a starting circuit including a starting resistor, starting capacitor, starting diac and starting diode. The transistors have their main current paths serially connected across an input capacitor to the circuit, coupled to the output of a rectifier system; the series connected transistors define a common middle junction to which a symmetry maintaining circuit, for example including two capacitors, is connected. The lamp itself is connected to the secondary of the lamp transformer which has its primary winding connected between the common middle junction between the transistors and the symmetry defining capacitors.